/*
    author:  Maksim1744
    created: 09.12.2023 11:45:03
*/

#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

#define mp   make_pair
#define pb   push_back
#define eb   emplace_back

#define sum(a)     ( accumulate ((a).begin(), (a).end(), 0ll))
#define mine(a)    (*min_element((a).begin(), (a).end()))
#define maxe(a)    (*max_element((a).begin(), (a).end()))
#define mini(a)    ( min_element((a).begin(), (a).end()) - (a).begin())
#define maxi(a)    ( max_element((a).begin(), (a).end()) - (a).begin())
#define lowb(a, x) ( lower_bound((a).begin(), (a).end(), (x)) - (a).begin())
#define uppb(a, x) ( upper_bound((a).begin(), (a).end(), (x)) - (a).begin())

template<typename T>             vector<T>& operator--            (vector<T> &v){for (auto& i : v) --i;            return  v;}
template<typename T>             vector<T>& operator++            (vector<T> &v){for (auto& i : v) ++i;            return  v;}
template<typename T>             istream& operator>>(istream& is,  vector<T> &v){for (auto& i : v) is >> i;        return is;}
template<typename T>             ostream& operator<<(ostream& os,  vector<T>  v){for (auto& i : v) os << i << ' '; return os;}
template<typename T, typename U> pair<T,U>& operator--           (pair<T, U> &p){--p.first; --p.second;            return  p;}
template<typename T, typename U> pair<T,U>& operator++           (pair<T, U> &p){++p.first; ++p.second;            return  p;}
template<typename T, typename U> istream& operator>>(istream& is, pair<T, U> &p){is >> p.first >> p.second;        return is;}
template<typename T, typename U> ostream& operator<<(ostream& os, pair<T, U>  p){os << p.first << ' ' << p.second; return os;}
template<typename T, typename U> pair<T,U> operator-(pair<T,U> a, pair<T,U> b){return mp(a.first-b.first, a.second-b.second);}
template<typename T, typename U> pair<T,U> operator+(pair<T,U> a, pair<T,U> b){return mp(a.first+b.first, a.second+b.second);}
template<typename T, typename U> void umin(T& a, U b){if (a > b) a = b;}
template<typename T, typename U> void umax(T& a, U b){if (a < b) a = b;}

#ifdef HOME
#define SHOW_COLORS
#include "/mnt/c/Libs/tools/print.cpp"
#else
#define show(...) void(0)
#define debugf(fun)   fun
#define debugv(var)   var
#define mclock    void(0)
#define shows     void(0)
#define debug  if (false)
#define OSTREAM(...)    ;
#define OSTREAM0(...)   ;
#endif

array<array<array<int, 2>, 105>, 105> dist;

int main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL);

    int x, y, p, qq;
    cin >> x >> y >> p >> qq;
    const int inf = 1e9;
    for (auto& a : dist)
        for (auto& b : a)
            b.fill(inf);

    queue<tuple<int, int, int>> q;
    q.emplace(x, y, 0);
    dist[x][y][0] = 0;
    while (!q.empty()) {
        auto [lx, ly, where] = q.front();
        q.pop();

        int cx = (where == 0 ? lx : x-lx);
        int cy = (where == 0 ? ly : y-ly);
        for (int mx = 0; mx <= cx; ++mx) {
            for (int my = 0; my <= cy && mx + my <= p; ++my) {
                if (cy-my > cx-mx + qq && cx-mx > 0) continue;
                int nx_lx = (where == 0 ? lx - mx : lx + mx);
                int nx_ly = (where == 0 ? ly - my : ly + my);
                if (dist[lx][ly][where] + 1 < dist[nx_lx][nx_ly][where ^ 1]) {
                    dist[nx_lx][nx_ly][where ^ 1] = dist[lx][ly][where] + 1;
                    q.emplace(nx_lx, nx_ly, where ^ 1);
                }
            }
        }
    }

    int ans = inf;
    for (int u = 0; u <= y; ++u)
        ans = min({ans, dist[0][u][1], dist[0][u][0]});
    if (ans == inf) ans = -1;
    cout << ans << '\n';

    return 0;
}